1. Field of the Invention
The invention relates to a microswitch with an integrated circuit, having two Hall sensors, at least one evaluation circuit, and a permanent magnet disposed fixedly below the two Hall sensors, the permanent magnet being oriented with one pole toward the two Hall sensors and having field lines penetrating the Hall sensors, a ratio of magnetic flux in each of the two Hall sensors being ascertained through the evaluation circuit, and a switching signal being derived from a change in the ratio upon an approach of a ferromagnetic tripping body.
One such proximity switch is already known from German Patent DE 42 11 486. However, that switch is constructed as an on/off switch.
2. Summary of the Invention
It is accordingly an object of the invention to provide a proximity switch with three switching positions, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and with which the status of a lock cylinder in a motor vehicle door is to be sampled for a central locking system. Three states which are to be detected are: cylinder in repose, rotated to the left and rotated to the right (opening or closing of the vehicle doors).
With the foregoing and other objects in view there is provided, in accordance with the invention, a microswitch with an integrated circuit, comprising a ferromagnetic tripping body being movable between three switching positions; two Hall sensors being associated with the tripping body; a permanent magnet disposed fixedly below the two Hall sensors, the permanent magnet having one pole facing toward the two Hall sensors for generating field lines penetrating the Hall sensors; and a dual evaluation circuit for ascertaining a ratio of magnetic flux in each of the two Hall sensors and for deriving a switching signal from a change in the ratio upon an approach of the tripping body, the dual evaluation circuit having first and second outputs, and the dual evaluation circuit changing a switching state with respect to one of the outputs in reaction to a positive or negative difference in magnetic flux between the two Hall sensors, for switching an occurrence of a vanishingly small difference, a positive difference and a negative difference in magnetic flux through the three positions of the tripping body.
In accordance with a concomitant feature of the invention, the tripping body is secured to a lock cylinder of a motor vehicle door; the tripping body is located centrally above the two Hall sensors in a position of repose of the lock cylinder; and by rotation of the lock cylinder the tripping body can be brought into an eccentric position relative to the two Hall sensors, so that three respective switching positions of the microswitch correspond to the lock cylinder in a position of repose, in a position rotated to the left and in a position rotated to the right.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a proximity switch with three switching positions, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.